1. Field of the Invention
This invention relates to the technical field of a laser output control unit, which controls output of a light beam such as a semiconductor laser.
2. Description of the Related Art
In recent years, as CDs (Compact Discs) and DVDs (Digital versatile Discs) have spread widely, and a recording and reproducing device used to reproduce information recorded on those optical recording medium have been developed. Then, there is a demand for technology for recording data stably on the optical recording medium and technology for reproducing data recorded on the recording medium stably.
In particular, semiconductor leaser used to record and reproduce data on optical on optical disc drive is also used as light source in other technical field such as technical field of optical communications systems and image forming apparatus. In using semiconductor laser, these apparatus are generally equipped with a laser output control unit to control laser output appropriately.
One of typical control methods for the laser output control unit is an average APC (Automatic Power Control) method that performs negative feedback control of laser output based on as average value of the laser output.
For example, according to average APC method, in a case of controlling the output of laser beam to record data on a DVD disc and reproduce data recorded on the DVD disc, the laser beam emitted from a semiconductor laser based on write data to be written on the DVD disc is detected by a monitoring photodetector. Then, average value of light beam intensities is calculated over a certain period of time based on the light beam intensity of the detected laser beam, and negative feedback control is performed with respect to output level of the laser beam emitted to the DVD disc based on the calculated average value of light beam intensities and a preset target light beam intensity of laser beam (see for example, Japanese Laid-Open Patent Application No. H 11-339398).
However, in the case of performing negative feedback control as the described above, the conventional average APC method is not capable of independently setting intensity levels and irradiation times of different laser beam. In other words, the conventional average APC method is not capable of maintaining independence of individual intensity levels.